Synthesis and characterization of novel fluorinated polycarbonate negative-type photoresist for optical waveguide

•Using fluorinated epoxy-terminated PC prepared stability photo-cross-linked film.•The film owned good thermal, optical properties and controllable refractive index.•The materials to fabricate various waveguide devices by direct-write UV technique.•The morphology and surface roughness of the lateral ridge was got by AFM and SEM.•The propagation loss of the channel waveguide was only 0.25 dB/cm at 1550 nm.

A kind of fluorinated and epoxy-terminated low-molecular-weight bisphenol A polycarbonate (FBPA-PC EP) was synthesized by solution polymerization of 4, 4′-(hexafluoro-isopropylidene) diphenol (6F-BPA) with triphosgene (BTC) and further reacted with epoxy chloropropane. The structure of the polymer was confirmed by FTIR, 1H NMR, 13C NMR and 19F NMR spectra. A series of negative-type fluorinated photoresists (NTFPs) were prepared by mixing of FBPA-PC EP and FSU-8 with triphenylsulfonium hexafluorophosphate and cyclopentanone as the photoacid generator (PAG) and solvent. The polymer films prepared from NTFPs by UV-curing exhibited superior chemical resistance, excellent thermal stability (Tds ranged from 295 to 303 °C) and low surface roughness. A clear negative pattern was obtained through direct UV photo-cross-linking and then chemical development which can be used as high-quality channel waveguides (the roughness of the lateral ridge ranged from 21 to 32 nm (1 × 1 μm)). For waveguides with the polymethylmethacrylate as upper cladding, the propagation loss of the channel waveguides was measured to be 0.25 dB/cm at the monitoring light of 1550 nm.

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